This project has progressed over the last 30 years from collection and descriptive epidemiologic study of morbidity data on domestic animals seen at 23 university veterinary teaching hospitals in North America, to case-control studies of home environmental factors associated with canine cancer and lately, cohort study of morbidity and mortality among U.S. military working dogs (MWDs) who ever-never served in the Republic of Vietnam, 1968-1973. Investigations are now focused on human cohorts addressing hypotheses generated by earlier studies. Specific Vietnam studies are: 1) Re-analysis of a 1983 study of mortality among 82,000 West Virginia residents, who as military veterans received state sponsored bonus money during the late 1970s (half of the recipients served in Vietnam, 1964-1973); preliminary analyses shows significant excess deaths occurring within the Vietnam cohort as of 1995. 2) Mortality study of the cohorts of U.S. Air Force enlisted personnel serving at Da Nang, Tan Son Nhut, and three U.S. Air Bases located in Thailand as identified from all military orders issued authorizing promotion or permanent change of duty station in 1971 (approximate populations are 8,200, 8,900, and 14,000 respectively). Expected deaths for analysis approximate 615, 668, and 840 respectively, based on the West Virginia cohort mortality rates. This investigation will examine if service at Da Nang AB, site of Ranch-Hand initiation flights which sprayed herbicides over I Corps, is associated with increased cancer incidence versus service at Tan Son Nhut, site of Ranch-Hand initiation flights until the end on 1966, versus service in Thailand where no herbicide spraying missions were initiated. 3) Cohort mortality study of military dog handlers and other military police who served in Vietnam (N=9,800) or elsewhere (N=8,500) as identified from a thorough review of MWD service records and other available military unit general orders issued 1967-1973. This investigation will examine if specific conditions identified in apparent excess among MWDs [histologic review of surgical and autopsy specimens (based on a standard protocol) was performed by the Armed Forces Institute of Pathology] likewise occurs excessively in companion humans (i.e., is the military working dog a sentinel for subsequent human medical conditions based on shared Corps area of service, military unit of service, or having worked with the specific handler?). About 1,000 dogs served and died in Vietnam with autopsy review; there are 2,700 handler-dog pairs identified. Service elsewhere, 1967-1973, is represented by 9,500 handler-dog pairs involving about 1,600 unique Vietnam-era dogs and 200+ Vietnam veteran dogs.